Cognitive psychology of perception Flashcards
What is sensation?
The process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted
What is perception?
The process by which sensory information is actively organised and interpreted by the brain
What are the parts of the human perceptual system?
- Each sensory information has a specific stimulation (e.g. light, sound wave)
- Stimulant is encoded by a specialised sensory organ (e.g. eyes, ears)
- The output from the organ is processed by dedicated brain areas (e.g. visual cortex, auditory cortex).
What are the five senses?
Sight Hearing Touch Smell Taste
What other senses are there?
Balance and acceleration
Temperature
Kinaesthetic sense
Pain
How do we see?
- Light travels through the eye and focuses on the retina
o Electromagnetic light energy is converted into neural electrochemical impulses
What are rods?
Visual receptors that respond to dim light - rhodopsin - very sensitive: - scotopic (night-time) - achromatic (120 million)
What are cones?
Visual receptors involved in colour vision. Most humans have 3 types of cones. - chromatic (red, blue or green) - opsins-less sensitive: - photopic (day-time) (7 million)
What 3 things do we see?
Hue, brightness, saturation
What is hue?
Visual experience specified by colour names and related to the wavelength of light.
What is brightness?
Lightness and luminance; the visual experience related to the amount of light emitted from or reflected by an object.
What is saturation?
Vividness or purity of colour; the visual experience related to the complexity of light waves.
What is the retina?
Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.
What is the Boynton illusion (colour filling the gaps)
- From the distance the yellow should fill in the gaps
- Poor colour resolution of cones at distance
- Illusion based on the resolution you have for colour processing
- Shows that colour resolution isn’t very good at a distance
What is the blind spot?
Essentially a hole in vision where the light hits part of the eye with no light receptors
Name 2 parts of the ear help us to hear?
The cochlea & hair receptors
- Contains the basilar membrane on which hair cells are located. The hair cells respond to sound pressure and transduce vibration into neural signal
What are the stimulus characteristics of sound?
- Wave frequency → Pitch
- Wave amplitude → Loudness
- Wave form → Timbre
- Audible sound frequencies: typical human range about 20 Hz to 20,000 Hz
What is the absolute threshold?
The smallest quantity of physical energy that can be reliably detected by an observer
What is the difference threshold?
- The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compares
- Also called Just Noticeable Difference (JND)
What is signal-detection theory?
- A psycophysical theory that divides the detection of a sensory signal into a sensory process and a decision
1) Response: “Present” & Stimulus is Present = Hit
2) Response: “Present” & Stimulus is Absent = False Alarm
3) Response: “Absent” & Stimulus is Present = Miss
4) Response: “Absent” & Stimulus is Absent = Correct Rejection
- E.g. snake or garden hose? When you have the snake, you are better off saying it is present than just a garden hose because you won’t die in the false alarm box, but might in the present-miss box
What is bottom-up processing?
Information processing in which individual components or bits of data are combined until a complete perception is formed
What is top-down processing?
Application of previous experience and conceptual knowledge to recognise the whole of a perception and thus easily identify the simpler elements of that whole
- Perception is not automatic from raw stimuli
- Processing is needed to build perception
- Top-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another
What is Gibson’s Theory of Direct Perception (bottom-up)?
- The information in our sensory receptors is all we need to perceive anything
o Do not need the aid of complex thought processes to explain perception - Use texture gradients as cues for depth and distance
o Allows us to perceive directly the relative proximity or distance of objects - (could be better placed as evidence for top-down processing) Instead of asking “What is perception?”, Gibson asked “What is perception for?”
o Perceive opportunities for behaviour
o Affordances (a pen = writing)
What is the Gestalt View of Perception?
- Basic tenet
o “The whole is more than a sum of its parts” - Law of Prägnanz
o Individuals organise their experience in as simple, concise, symmetrical, and complete manner as possible
What do Gestalt principles do?
Organises perceptual inputs into unitary forms
What are the 6 Gestalt principles of grouping?
Proximity Similarity Closure Good Continuation Common Fate Good Form
What is the Gestalt principle of perceptual organisation: figure-ground?
Organization depends on what we see as figure (object) and what we perceive a ground (context).
What is the Gestalt principle of perceptual organisation: similarity?
Objects that have similar characteristics are perceived as unit.
What is the Gestalt principle of perceptual organisation: proximity?
Objects close together in space or time perceived as belonging together.
What is the Gestalt principle of perceptual organisation: continuity?
We tend to perceive figures or objects as belonging together if they appear to form a continuous pattern.
What is the Gestalt principle of perceptual organisation: closure?
We perceive figures with gaps in them to be complete.
What does relative perception consist of?
- Contrast
o Occurs when stimulus are in close proximity (space or temporal)
o Changes sensitivity to seeing a difference - Our senses respond to the environment around the stimulus we perceive
What is depth perception?
The ability to see the world in three dimensions and detect distance
- Vision only has a two-dimensional view
- We must interpret the information given to perceive depth
- We take flat images and create a three-dimensional view
- Optical illusions demonstrate that this interpretation does not always have to be correct
What are monocular depth cues?
- Texture gradients - Grain of item
- Relative size - Bigger is closer
- Interposition - Closer objects are in front of other objects
What is the Gregory’s theory?
The visual system makes hypotheses about distance to objects based on evidence in the image. Interpretation of size follows
E.g. in the Ponzo illusion, you may interpret the horizontal lines as indicating depth and so the images formed on the retina by the two horizontal lines is the same. But, you perceive the upper line as longer because you think that it is farther away
How does perception develop?
- Some innate abilities but improves with age
- Infants < 1 month can detect changes in brightness and follow moving objects
- But poor acuity and poor colour vision
What is the visual cliff?
Glass surface, with checkerboard underneath at different heights
- Visual illusion of a cliff
- Baby can’t fall
- Mum stands across the gap
Babies show increased attention over deep side at age 2 months, but aren’t afraid until they can crawl (Gibson & Walk, 1960)
What are critical periods in perception?
- If infants miss out on experiences during a crucial period of time, perception will be impaired.
- When adults who have been blind since birth have vision restored, they may not see well
- Other senses such as hearing may be influenced similarly.
how can context influence perception?
- The same physical stimulus can be interpreted differently
- We use other cues in the situation to resolve ambiguities
What do illusions do?
- Illusions highlight that we interpret the world
- Impossible figures are difficult to process as the brain tries to interpret a possible image
- Some figures can have multiple interpretations but we can only see one at a time
